As kosst_amojan mentions, there is a metallic clicking sound right after I fully power off my Pass XA-30.8 (which does not happen when I put it into standby).
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Is the popping coming from the unit or through your speakers. I have owned an x 250.5 for 11 years now and it will clink when it is warming up or cooling down. I think this is from the heat sinks expanding and contracting from the heating/cooling cycles of being off and on. It the sound is through the speakers then ya, a cap up the chain somewhere could be going or a tube
Have the same issue with my INT-30, figured there was something defective with the amp as I bought 2nd hand, although SQ not affected beyond the momentary interruption from the noise itself. What stumped me is that it would happen even when the unit is unplugged from power source. My observations:
1. The sound is a sharp metallic "ping" or "pop" - sounds like metal contacting metal.
2. It can occur even when no power to unit, so must be mechanical not electrical.
3. Ping occurs 1-3 times over 5-10 mins when amp is turned on, but does not occur when fully warmed up. Same sound at similar intervals when unit is powered off and cooling down.
Conclusion: The sound is the result of the expansion and contraction of the external heat sinks bolted to the amp chassis, which is why it's heard only during warm up and cool down, but not after running for 15 mins or more. At least that's my best guess given the above symptoms. Since the amp sounds great otherwise I've decided to view it as a lovable quirk and instead of an exceedingly minor annoyance.
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!