Judder and belt squeak when pulling away, manual box

[Black9]

Have a 54 Golf GTi with manual box and 85K on the clock. Clutch seems fine, no slip and feels light just like every other VW I've driven. But when pulling away using what I'd say a normal and adequate amount of throttle there's a slight vibration and squeak coming from the engine area though when I pull away with more throttle there's none of this. Also this doesn't happen in reverse either? 

Any ideas what this could be, start of DMF troubles possibly?

[bacillus]

I would first check the grommets securing your engine cover to the engine as one could be missing or perished.

[Black9]

The engine cover seems to be quite loose and rattles a bit. Could this be the culprit? Also the belt only really squeaks when it's raining?

[bacillus]

The cover when secured properly is a bugger to move, let alone take off so something isn't right there.

As for the squeak, I would check the tension in both the cambelt and auxillary belt that drives the ac compressor.