Try and remove the oil filler cap with the engine running.If it is a struggle,and there is a lot of "hissing",then it is very likely the engine breather is faulty.It is part of the oil filter housing .Not a cheap or easy fix.I think the parts are cheaper from a Volvo dealer.

I played the clip to an office colleague who has a 10-plate Focus ST: he immediately said 'oil diaphragm' as it's apparently a known weakness on the ST.

His advice is get it looked at and changed quickly, and don't drive the car far, or fast, until it is changed because there's a risk of blowing oil seals.

If you google 'Focus ST Oil Diaphragm' there's plenty of information, including part numbers and how to change the component yourself. It can be done but will take an hour or two. Parts cost seems to be around £200, and as the Doc said above, it's worth checking the price from Volvo dealers against the Ford prices.

Edited by craig-pd130 on 30/03/2017 at 10:10

Sounds as though coming from the front of the engine. Possibly a failing pulley bearing? Suggest take the front covers off if you can and have a look, listen and feel for hot belt/bearings. The sound can change going from cold to hot. Age? Miles?