AD30HTC Gain???

[boiler]

I just got the ad30tc head and it's OK, but when i connect it with a marshall 4x12 cab. and then turn the gain above half its starts to make strange noises like my speakers are torn apart..
I did connect it to a bassman 2x15 cab. and it was OK, but with a vox cab. it did the same.. I checked the marshall cab and it works fine!
I don't get the problem here, it seems there is a problem with the gain.. normally the marshall (280W) should be able to handle the 30 W amp?
When i play through a big muff, and less gain it's OK.
Anyone please help me to solve this...
Thanks

[boiler]

Yeah, the impedances are both 16 ohm...so that should be OK..
The distributor thinks it happened during transport..some valves or the printplate isn't into its position ??
Steven