Ehiem Classic 350

[nortonmad213]

hi so i have my tank set up with a ehiem classic 350 and the water is crystal clear

bargain
the only problem i have with it is getting all the air out of the filter media,
it will run quiet as a mouse for ages then all of sudden starts shuddering and sounding really loud,
then it will clear as the bubbles come out of the spray bar and then its quiet again.
i was wondering how i can solve this as it has  woke me many times now, starting to get annoyed as ehiem has come really highly recommended
thanks in advance

 

[Blobfish]

How long has it been running for?

 

[nortonmad213]

3 months

at the start i could tip it from side to side to empty the filter of air and it would be fine,
now its just residual bubbles popping throug occasionaly.
couldn't be sucking in from my air wall?