Hey people!

Total Noobie to this sort of thing and I seem to of found myself dumbstruck! Apologies if this is a recurring issue/ topic of conversation!
I have recently reinstalled my onkyo 706 reciever and plugged it all in.. I have kef 2005 speakers on the front , left and right with the sub that comes with that and kef 1001 on surround left and right .. long story...

Now when I fired it up it seems my front right is popping occasionally and sometimes the left too, very rarely the centre.. I have decent cable and it's all new and correctly terminated as far as I can see.. correct polarity also.. I thought it was interference so I removed all other items so now it's just receiver and sub.. I thought it could be the optical cable so removed that.. still happened.. now I tried it on radio and it seemed to of stopped?
Is there anything I am missing or can try before resigning it into the garage??

Many thanks for any guidance and apologise for any ignorance!