Unusual noise in VW Golf diesel

Hi
Have a 2001 VW GOLF,TDI,MK IV,100K miles. Approx 3 weeks ago a loud "sizzling" noise started approx 1 min after car was started and continues for about 10 mins until car warms up and then stops. It always happens on a cold start in the morning and sometimes when car is started during the day. The noise gets louder when the car is revved up.
The fan belt was changed during service, tensioner was not changed as it was OK but noise issue remains. Timing belt and tensioner was changed at 80K miles. When I look under bonnet noise appears noise appears to originate from Left hand area where fan belt, diesel filter, Brake fluid resevoir and power steering resevoir are located but can't find source of noise.

Any Ideas

A lot of the vw engines do that from a cold start I wouldn't worry about it too much.For peace of mind you could get the alternator belt removed and check the tensioner bearing for rumbling/slackness.Even give the cold engine a short run without the belt and see if it sounds any better.