Running water noise / Starting trouble

I've been having some trouble recently with my 1997 Megane 1.6RT Sport.

First we noticed a running water sound which seemed to come from around the passenger footwell. I can't hear this when I'm outside the car or looking under the bonnet, only when I'm inside.
Somebody suggested it might be the Heater Matrix, but I'm not sure. (?)

The other thing is that the car is very lumpy when starting but after it's sorted itself out it runs fine and drives nice.
There was some cream in the oil cap too, which immediately worried me (Head gasket I wondered)

I took the car to Renault and they did a diagnostic check.
They advised that compression was down on the 2nd cylinder and reckoned it could be a tight tappet or the head gasket.

Also, recently when starting the car sometimes half turns over, when I try it again it usually works but the mileage on the trip thing is set back to 0.00......??

Any ideas anyone, please???