Sounds like a belt going, but which

Disclaimer - I know very little about engines so guessing here

Sitting in traffic, quite a loud sound that lasted for about 5 seconds, wasn't the heater as it was off, sounded something rubbing and unhappy

Noise then went away and didn't come back until I hit the dual carriageway and every 5 minutes or so would hear a sound like a motorbike going past (no, I looked each time, no bike)  it was quieter than before.

I had the cam belt replaced about 5 months ago, so that leaves me (guessing time) fan belt or timing belt

Any ideas as to what I could check to confirm?

Thank you

Any temperature issues? Could be water pump bearing

Could be your fan on the rad ?

I had to change out the fan on the rad because when it kicked in it sounded like a chainsaw trying to cut through a 50lb sack of bolts! 

If it screams like a banshee, then check and adjust the alternator belt if not done already.
Had that as well and it was so intermittent it drove me made for about a week. 

Until common sense prevailed!    
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