crazy amp problem

[Garthplinko]

For lack of a better forum, I'm posting my question here.

so I'm tracking a band and we're having a sound come through the amp that sounds like a helicopter. Not real loud - the playing seems to mask it, but I don't really want to use a defective or broken amp on the recording...it just doesn't sit right w/ me. The amp is an Engel Savage 120 and it's relatively new (and it's the second one the guitar player has had since his first one BLEW UP).

Here's what we have noticed so far:
- if you put the amp on standby and turn it back on it goes away UNTIL the first powerchord or loud signal hits the amp and then it's back and we can't get it to stop.
- my guess is that the problem is somewhere in the preamp stage somewhere because the tone of the helicopter sound IS affected by outboard gear in the effects loop.
- I don't think the problem is because of a crappy electrical outlet - it's plugged into a Furman and the other head he has isn't making the noise.
- It's not the guitar, because other guitars produce the same problem.

Anyone have a problem like this before or suggestions how to fix? If so, much appreciated.

[oldguitars]

start swapping tubes. also, lose the FX loop. i bet he doesn't need it.... : )

[Garthplinko]

I dug and finally found this - does this make sense?

http://www.geofex.com/ampdbug/mtrboat.htm

Tube swapping isn't a bad idea at all - I will try that next.

[emrr]

Motorboating was the first thing I thought of, and that's either failing power supply capacitors or poor design.

[GooberNumber9]

I'd say bring the signal chain back to basics, guitar -> cable -> amp. Change out at least the power tubes. If the problem persists (sadly, I think it will) then you've probably got bad caps. Take it to a pro. If it's that new, activate the warranty, or return it for a refund.

Good Luck!

[???????]

I thought motorboating as well.

[drumsound]

What effects are in the chain? Rotovibes are famous for this noise. Is there tremolo in the amp? It could be the culpret.