Hi,
mine does this currently (well it sounds like it's the same as yours). However the cause is basic (in my case), so please excuse me if I mention something obvious that you are probably already quite aware of. I'll mention it just in case...
Are the sounds in the patches different every time you switch it off and on?
Can you program a patch to make it make a sensible noise, even if lost after a power cycle?
Because that's what mine does currently. It has no battery backed RAM and so on any power cycle it loads up with random junk. Some patches make weird noises, some do nothing. But you can program it to make sounds, because it is essentially working fine in that respect.
I thought mine was broken, so did the previous owner, so they gave it to me many years ago. I've not used it since but the HAWK kit will be breathing a new lease of life into it soon :)
I suspect your Poly has got the battery powered RAM, so it's something more complex.
But just in case...
All the best, Louis