Can you elaborate a little on the nature of this "sizzling" noise and how it manifests? From what I can tell, you could mean one of three different things:
1) "When I transmit, I can hear a sizzling sound coming from inside the amplifier."
2) "When I transmit, people tell me there's a sizzling sound in my transmitted audio (even when I'm not talking -- i.e. I just hold the key down, and you can hear a sizzling/crackling sound)."
3) "When I transmit, people tell me my audio sounds "sizzly," i.e. my voice is distorted such that it seems very grainy and/or crunchy."
Is it one of those things? Is it a combination of those things? Is it something completely different? Inquiring minds want to know.
If it's number 3, I think it means the amp is being driven with too much input power, pushing it into non-linear operation. This can cause a lot of clipping and distortion. It may get worse as you talk more because the transistors get hotter and the non-linearity becomes even worse.
If it's 1 or 2, then it could be a problem with the power supply. The regulator might be failing and causing the voltage to climb too high. (You should be able to confirm this with a voltmeter.) Or there might be some kind of noise or hash on the supply voltage that's being translated into noise on your transmitted signal. You didn't say if you're running the radio off the same power supply. If you are and things are fine with the amp off, then either it's not the power supply or it's a problem that only manifests when the amp loads it down.
From what I can tell googling around, the Pyle 35 amp power supply looks like a decent quality unit so I'm not inclined to blame it.
My money says that either the amp is being over-driven, or else there are still some failed or intermittent parts left behind from when that 2879 blew up. (But that's just an armchair engineer's opinion.
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-Bill