My Pentas pop too. They always have.

When I say pop it isn't something that can be lived with, it's more of a loud crack I guess and sounds like it will be doing some sort of damage.  One of my others has a quiet pop but nothing like this and as with yours peeps, totally acceptable.

So the loud Pop or crack has been resolved. I substituted various assemblies to isolate the problem which was isolated to PCB 22. Diodes and resistors all checked and no faults. So identified as IC2 chip.  Cost about £0.40! But postage et al was about £12! So I ordered a few in case anyone wants any? Chip replaced and after assembly, the pop/crack has gone. Of note the input switch does produce some interference when modulated with the speaker running, with the switch in a position there is no interference.  That may have indicated the switch was at fault.  When diagnosing the problem I substituted the door with a know good one and still had the pop/crack.  Contact cleaner was spayed into all switches. I have spare IC2 Chips if anyone needs them, cost of packing and post plus the £0. 40!   I hope this post helps someone diagnose similar problems. Nick

Somewhat late, but there a detailed post on the old forum which echoes and adds to this useful post. See https://archivedforum.beoworld.org/forums/t/14677.aspx