Crackling/Distortion noise when I turn up volume.

A dirty volume pot. could be the culprit, a squirt of "electronic contact cleaner" sprayed in the volume control pot should solve it

Hi Greh, I had the same problem as you with an old Audiolab 8000s amplifier. In my oppinion (and I would say I am pretty sure) it is a potentiometer problem. I sent the unit for repair, and they found a small imbalance between left and right channel that came from the potentiometer (ALPS blue pot). They changed it but the imbalance is still obvious and not only in the lowest listening level but at almost all volume settings (and yes, I paid the ridiculously high amount of $300, 150 of which were of course refunded). I only use one source and so I built a small passive preamp that I now plug directly to the power amp section and the problem is solved completely. Of course there are many other drawbacks with the passive (but also some advantages...).
If you do not want to go this way, what you could do is to change the potentiometer inside your amp with a better one, or an attenuator (i.e.DUCT) at best. I would be pretty sure that your problem (both imbalance and cracking noise) will be eliminated. Let me know if you need more info and good luck...

Forgot something...You say that your dealer found nothing wrong but bear in mind that all potentiometers have an imbalance tolerance and that is maybe why he did not mention anything. I am not aware of any highly commercial pot that does not have an imbalance. Due to their construction, attenuators on the other hand have extremely small imbalances (0.05db maybe) and that is why I recommended you go this way. As for me, in the passive I built, I bought a Sfernice potentiometer that costs in the UK $50 (twice the price of the ALPS blue pot) and I am satisfied with it. There is of course still a very small imbalance but it is far way better than before...