I had something similar on my old giulietta multiair after I did a timing belt and water pump change. in my case it was the brand new genuine water pump (valeo). I removed it it inspect it and one of the o rings that sealed the rotating shaft hadn't been installed correctly and was bulging up slightly. I ended up throwing it the bin and putting the old one back in.
Cons: o-ring defect, faulty installation
Vehicle:
Alfa Romeo Giulietta
