What is this noise?

[DonTom]

I am working on my RV. I am doing a rather major tune-up and changing hoses, Serpentine belt, wires, spark plugs, distributor cap and rotor, thermostat, ignition coil, etc.

It's a year 2000 Express Van, 7.4L MPFI engine.

Battery is completely removed because I will be changing it also.

While working on it, I am hearing a rather loud noise, kinda like a hum perhaps every minute or so and it lasts about 15 seconds. Varies in pitch. It seems to be coming from the left top of the engine. Sounds very electrical, but the battery is on the ground outside the RV. I just cannot figure out what this noise could be coming from.

Engine is NOT running, of course, when I hear this noise.

I am not really worried about it, but it seems rather loud when it happens and the battery has been out of the RV for more than a week.

Without a battery, what can be making such a noise?

-Don- Auburn, CA

[Ken]

I'm really guessing in the dark here, Don. Does
your RV have two batteries? Does it have a
battery charge splitter dividing the charge
between the engine battery and a 'house'
battery. If so the noise might be coming
from the alternator. Use a screwdriver
or length of wooden rod as a 'listening
post'.

FWIW.

Ken.

[DonTom]

I'm really guessing in the dark here, Don. Does
your RV have two batteries? Does it have a
battery charge splitter dividing the charge
between the engine battery and a 'house'
battery. If so the noise might be coming
from the alternator. Use a screwdriver
or length of wooden rod as a 'listening
post'.

FWIW.

Ken.

It does have house batteries but the disconnect switch has them disconnected.

I am beginning to think it could be some type of an alarm with a very well hidden small battery.

The noise seems to be coming from under the intake manifold. It stayed on for a couple of minutes today. I have never noticed this noise when the battery is connected.

And it is not a weak noise. It's fairly loud. It is NOT coming from near the alternator as the noise is weaker towards the front of the engine where the alternator is located.

-Don- Auburn, CA

[DonTom]

Mystery solved!

The noise stayed on for more than five minutes today, so I had plenty of time to find it. The noise was coming from GM part number 15150325, which is not in the engine, but on the firewall making it sound as if it is coming from the engine. Where it is getting its electricity from is still a mystery, as well as why it makes so much noise, but I at least now know where the noise is coming from. I disconnected it to stop the noise.

It controls the internal lights, but is mounted on the firewall just above the left side of the engine.


-Don- Auburn, CA

[DonTom]

I was going to edit the above post, but the edit function is not now working for me. It just gets stuck on a wait symbol.

Anyway, what I was going to add is that I was able to easily take the PC out of this module without doing any damage to see what makes the noise. On the bottom of the PC board, there is a relay, so it clicking off and on very fast has to be the reason for the noise. Why this happens when the battery is removed is a big mystery to me, but I guess I really have no other reason to even care, as long as every works okay, which it does, including all the interior lights. At least it all worked normally before I removed the battery.

-Don- Auburn, CA

[Ken]

Fingers crossed that it all works OK when you have everything back together.

A relay can only buzz when powered up so either it has its own source
or it is related, somehow, to the house battery. I believe this is the case,
as it is the Interior Lamp Control Module.

re,. the edit problem. call up 'edit', edit the post, click on the 'Go Advanced'
button and Submit Reply from there. It works for me.

Ken.

[Ken]

Um!, I may have misunderstood your comment regarding the 'edit'
facility, Don. I think I have the same problem as you in that the
SWC (Spinnning Wait Circle) now starts as soon as one selects
'Edit'. I used to get the problem when trying to post the edited
version.

I think someone has been tinkering with the software. I'll have a
look but I don't think it is anything I can change.

Ken.

[Ken]

Message regarding the 'Edit Post' facility.

It would appear that the 'Edit Post' facility
is not working properly. I've had a look in
so far as my Admin permissions allow but
cannot identify the cause of the problem.

I will let Eric know.

Ken.

[DonTom]

Fingers crossed that it all works OK when you have everything back together.

A relay can only buzz when powered up so either it has its own source
or it is related, somehow, to the house battery. I believe this is the case,
as it is the Interior Lamp Control Module.

re,. the edit problem. call up 'edit', edit the post, click on the 'Go Advanced'
button and Submit Reply from there. It works for me.

Ken.

Nope. Class C RV's are made from vans. The lighting upfront in the cab comes from the chassis battery only, and that is removed. The lights in the "house" section get their battery power from the RV house batteries.

The cab is all stock stuff. Nevertheless, the voltage for the light module has to be coming from somewhere. Later I will put everything back together and remove the house battery connections--which the battery disconnect should be doing anyway.

I just now remembered something as I am typing that totally solves the mystery! Something I added!

I have solar on both, the house batteries and the chassis battery. Obviously, the voltage is coming from the 15 watts solar for the chassis battery. I have another 80 watts of solar for the house batteries. As the relay kicks in, the solar voltage will drop from the load and release. This will happen so fast that the relay becomes a buzzer! The small solar controller probably has something to do with the timing of every minute or so.

While I have a way to turn off the house battery solar, I never installed a way to turn off the chassis battery solar. I will add a switch in series with it so this never happens again. I hope the relay is still okay, but even if not, it's a cheap easy to replace part.

Now the mystery is all totally solved. I bet if I worked on the RV at night, there would be no noise at all. But it's getting sunlight while I work on it.

-Don- Auburn, CA

[grouch]

Fingers crossed that it all works OK when you have everything back together.

A relay can only buzz when powered up so either it has its own source
or it is related, somehow, to the house battery. I believe this is the case,
as it is the Interior Lamp Control Module.
Ken.

Some relay assemblies have a capacitor inside. This lets them function smoothly. I haven't seen it often, but I have seen a few over the years. Especially if it has a vacuum reserve.

[DonTom]

I have the RV all back together and all is fine, including all the cab (and other) lights. With the chassis battery installed, I never have the noise as then the cab light is on and the solar is then not doing much other than very slightly reducing the load of the lamps.

-Don-