#1
The reverb in my Hartke GT60c is fairly weak, but if it's turned up over 2 there starts to be a slight high pitched whine in the tone. The tank is already mounted on a piece of plywood inside a tolex bag, and I used electrical tape to tape a piece of cardboard to the open bottom of the tank and it helped slightly. I also tried wrapping the tank in tinfoil but that didn't work at all, made it a lot more noisy. The tank is already in the far bottom right of the cabinet and can't be moved any further away from the output transformer. The wires to it are pretty thin so maybe they could be part of the problem. Anyways I've been using pedal reverb until I can get this thing quiet.

The tank is a Belton BS2EB2C1B, which is a cheap 9.25" two spring tank made in Korea. Accutronics makes a better quality 3 spring 9.25" tank, and the amp cab is about 20" wide so a 16" tank would fit too. I think it would sound better with a 16" Accutronics tank, but would it be any quieter? Other than the wires I'm not sure where else to look to quieten this thing down other than trying a tank switch.
#2
Get the accutronics - but if there's plywood, and if its mounted at the bottom (which apparently is a bad thing to do), it might not sound the best it can.

But then, my unit appears to be at the bottom, and I love my reverb (accutronics).
So, try a new one then.

Might quiten down if you get a quality reverb (the accu :P).
Sunn O))):
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- Fender '72 Deluxe Telecaster
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#3
clean all the contact points first and make sure it is not tube driven reverb which i doubt. i don't know Hartke's at all lol. Squeeky and whine may tell you your problem is circuit driven which may be hard to fix despite what pan you put in there.