Hi Andy,

May be worth temporarily swapping fronts and rears and see if the problem stays with the speakers or with the rear outputs.
You need to work out if the speakers or the processor is the cause of the problem.

Have you ever had the speakers serviced? Crackling noises from DSP5000s could be the start of the breakdown of the load resistors.

Let us know how you get on.

Cheers,

Steve

Main: 861v6 (LPS), 808v6, UHD722, DSP8000SE Anniversaries, DSP5200HC, DSP7200.2, SW1600, Sky Q, Cambridge Audio BD, Roon, M80
Office: 861v4 (LPS), 818v3, 800v4, HD621, M&K S150P, DSP5500HC, M&K MPS2810 sub x2
Son's system: 861v4, HD621, DSP6000.2, DSP5k.2C, DSP33, F80
Spare: MCD, 100 Series, 200 Series, 500 Series, C15s.