V6 Petrol unusual noise

[Tigmaster]

Hi
Now I have sorted my gearbox issues and serviced all the engine I am slowly working through some other faults.

One is a strange noise that only occurs when accelerating.
It doesn't do it all the time and I cant make it do it whilst parked.
It sounds like a cat meowing.
As soon as you take your foot off the gas it disappears. It doesn't do it all the time and seems to be more noticeable when cold.
Sometimes it sounds like a motor/pump is kicking in which could be making the noise.
I have checked the belts although it doesn't sound like a usual loose belt squeal. The V6 has an automatic belt tensioner on both auxilary belts and they seem to work ok. I removed both belts. The alternator/steering pump belt looks fine and the tensioner pulley seems ok.
The alternator belt has some fine cracks appearing so I will get a new one. The tensioner pulley doesn't sound noisy in terms of bearing gone but does sound a little bit dry. Could this be the cause? Can I replace the bearing on its own?
Alternator, steering pump and AC sound fine.
I am told it had the timing belt changed last year.
Just wondered if there are any other known issues causing this unusual noise.
I will see if I can capture it on video.

Regards
Sean