Preamp/interconnects cause amp problems?

My power amp, which sat, untouched for 3 years, always on and sounding great had a short in the power supply (cap gone bad?).

I sent it back to be fixed and and hours after getting back had the same issue. Manufacturer replaced boards and related pieces and is sending back but said they found nothing that they think would cause the issue.

so my concern is it’s something here causing it. Even though the manufacturer put the amp on the burn in rack for a week I’m worried it will have this issue again.

is it possible my preamp or interconnects could cause this? I have a loaner amp in place now for a few months and have had zero issues with it (same everything and save outlet)
but it’s a different (lesser) brand.
What exactly is going bad?

If it’s the power supply rectifier diodes or caps, it is more likely to be a bad incoming AC problem. If it were an amplifier board going bad more likely a preamp/speaker problem.

Also, exactly what amp is this? Is it DC or AC coupled inputs?

@erik_squires I honestly have no idea. I asked if I should get a Variac or something and he said no. In fact the tech said he wasn’t totally convinced it was a power issue. I know zero about amp building but that struck me as odd.
Essentially what was happening was, in the middle of the night while the system was off (save for the amp) loud popping sounds we coming from the speakers. I quickly flicked the amp off. It would start again once I turned it on and then 2-3 seconds later speakers popping loudly again.

after I got the amp back the first time the tech said they repaired the short and put it on the rack for a week then booked up a source and speakers and played it Iin the shop for a day. I only got it to play for a few hours before it started again.

it’s headed back to me and though my current amp has been fine I’m worried I’ll have the same issue again.
Post removed 
@dletch2 he did confirm the issue then repaired what was shorted and sent it back.  When I sent it back again he confirmed it happened again but couldn’t see what the cause was. So he pulled
and replaced the boards and the power supply. I’ve not paid a dime so far and I did offer to pay some shipping but he refused.

I just don’t want this to happen yet again because of something on my end. 
Post removed 
@dletch2 that was my thought as well. I just want to be sure. I haven’t popped a speaker yet and don’t want that streak to end
Just because the dealer could not find anything does not mean there is no problem. case in point, I bought a used preamp which had been at the mfg's service center for an issue which was supposedly fixed. The seller had it shipped directly to me. When I got it and hooked it up, the right channel quit working. Changing tubes didn't help. When I called the seller, he was shocked and said that it was the same issue he had sent it for repair. However when talking with the mfg, she too had left it running for a week trying to ;locate the issue and found nothing. I sent it back to her and declined the sale. Anyway, I learned later from the seller that it was a resister gone bad.

Some things happen like that and when your car has an issue that never shows when you take it to the mechanic. Life, I guess. The frustrating part
What model amp is this? Was everything OFF, not standby, that is connected to the amp when popping started? When you turn the amp off and then on again, has the preamp been on the whole time?
Preamp was off. 100% off. DAC and phonostage are always on 24/7.

when I turned it off preamp
Is always connected. Tried with nothing connected and also with a passive connected and same thing .
Sounds like for sure the power amp. The best way to troubleshoot problems like this is with freeze spray. Your tech should be aware of this technique. I have found failing pre-driver or driver transistors were the cause in some amps.
A bad resistor in the power supply can cause the popping sound you mentioned hearing at night some amps will do this when there are issues in the power supply. If the manufacture would of had speakers hooked up to the amp they would have heard this the first time it was on their burn-in rack, they also should listen and not just take measurements. 

This time around i'm sure they took their time and fingers crossed all should be good.
He did mention something about transistor(s). I’m afraid my ignorance on electronics means I didn’t fully
process what he said.

my hope is he fixed the damamge last time but not the cause; and that cause has now been eliminated. My temporary amp has been hiked up 24/7 with no issue.
Popping sound in the speakers is dc. The amp either has a transistor problem, which is easy to find, or a short at the output caused by a wire or component fault, which is difficult to find. Could be carelessness in manufacturing in which case it’s a lemon and I would go for a replacement unit.