Anyone else have problems with intermittent but regular static bursts?

I have changed power supplies using only the recommended Line 6 adapter. It hapens in all locations with all guitars and cables so I've eliminated all of the sources I can think of.

The amp is a Gabriel 18 watter and is clean as a whistle without the M-9 and with other pedals. When I first got it, radio interference was the problem. It was a bit better after authorized service, but sometimes still there.

Now it's unusable and I really rely on it.