Pass labs poweramps

I've a 350.5 with the same popping, clicking on powering up and off.  I spoke to a Pass Labs tech, he explained it's entirely normal. After shipping, the unit may have sustained some hard landings. To mitigate by perhaps 50% these sounds, he suggested after the amp has been powered on for a couple hours, to take an allen wrench, loosen and remove the front plate, and tighten (but not too much) the chassis screws inside. I haven't bothered with the fix; knowing that this is normal operation is OK w/ me.

All my Amps are Pass Labs X250 X260.5 and anX5 I would call the sound more like a single clink sound like water in an old radiator when it warms up. All this equipment I have purchased second hand and any time I have a question I have called Kent English or emailed him. He has always treated me like I just purchased the most expensive Amplifier they make Best service I ever had in or out of warranty. They STAND behind what they sell

Ditto on my X250.5 - definitely notice metal sorta clicking noise after powering down. I called Pass and they explained it was the thermal contraction in the heat sink causing the noise and that it was completely normal. This past weekend - i noticed clicking during warm up and got a bit worried. But glad to see I am not alone in noticing clicking during warm up. So far - it has not affected the SQ - its a solid performer otherwise!

Yes Folks...all that sound is ..just the amps cooling down..expansion of cooling fins returning to room temp.... NORMAL ALWAYS..no worry needed what so ever....!!!!  Rock On..!!!!

I've had an F5 for about a year. I've never heard any noise when my amp is warming up,or cooling down. Maybe I should get my hearing checked. :-)