Help! Bearing noise??

[orangeLP400]

I have a G reg 1990 Eunos 1.6 with only 70K miles...been hearing this bearing type noise sometimes when ticking over and definitly when the revs drop almost to tick over...sounded like alternator or power steering pump bearing to me but when i took a look it seems to be coming from under the cam cover and when i took off the oil filler cap it was much louder. Car is perfect otherwise and oil to level and clean. Advice/help from the MX5 gurus would be appreciated thanks.

[orangeLP400]

No this is not a tick tick noise that rises with revs, it is more of a metalic "squreeching" sound, like a dry bearing. Will investigate further next week. Thanks for your responses.

[orangeLP400]

No, not a fan belt slipping!! its a metallic squreeching, not that loud and can be heard on tickover and when revs drop ...as its louder when oil filer cap off i was wondering about the camshaft bearings or whatever they revolve in! have not taken cam cover off before so dont know what lies beneath but thought i would ask folk on here in case it was a common problem and i could get some direction. Have a manual at work so will investigate next week but all help and suggestions appreciated. Car runs fine, lots of power , starts first time, no other untoward noises. It is filled with standard shell oil, so as per suggestions here i may refill with fully synth.

[orangeLP400]

Thanks all for info...still had no time for further investigation but i think the suggestion that its the water pump would seem to make the most sense noise wise...will check it out and will comment.