i didnt know power supplys had speakers in them
Most of them do not, I agree with Rob, RF is getting back into the supply somewhere and by putting the big cap inline you are filtering it out.
Any Modifications done to the 2510?
If the limiter is disabled or modified and not properly adjusted along with the Amplified Mic may be contributing to the problem.
What happens if you push in the "mic gain" button in on the radio or reduce the mic gain on the turner?
The Amp meter going back on high power I would also say could be a sign that RF is getting back into the supply.
What voltage are you running?
Anything over about 14.8 volts into a Texas Star Amp will lead to Failure, they do not tolerate over-volting at all and will increase the chance that the signal is getting dirty coming out of the amp.
After that, as you have already said, just keep going over the whole system, grounds, the Choke that Rob talks about will help if CMC`s ( common mode currents , this is RF that is flowing on the outside of the coax) are letting stuff get back into the supply.