Nissan Primera P11-144 alternator belt noise

hello i have posted this before but can find the topic. i have a nissan primera p11 144 18s yr 2000 when i start the car there is a noise coming i think is the altnator belt. when under load how do i check it. i read somewhere that to spray pentrating oil on belt would that not cause it to slip more.

well ladies and gents any one have this problum. the belt seems tight mosty when i start up the engine from cold. for about 30sec to a min. then it dies down to a background noise you can still here it very slightly but it is still there thanks for any replyes pat.

i have/had this problem i thought it was old belts so had them changed for new ones but still had a noise, the only way i can get rid of the noise is a bit of chalk, hold a bit of chalk with long nose pilars on the sides of the belt and if noise goes away theirs your problem belt rubbing on the pulleys. i havent investigated to see if one of the pulley bearings are shot but mine comes and goes so not to fused at the minute .