'Noisy' rad, vented system, bleeding stops it but soon returns

[WaterTight]

What be the cause(s) and solution(s) pleaseeeeee?

 

[finchy01]

My guess sludge. It's probably not air but gases created by sludge in system. That'll also make it noisy. Obvious place to start I know but that's why I suggest that first.

 

[Rickster123]

What sort of noise? Like water rushing through it?

 

[Ch4 plumbing]

Could be the pump drawing air down the vent and filling the Rad every few days or the rushing noise could be the pump pushing through a nearly closed rad valve.

 

[WaterTight]

Think I need to actually hear it. Thanks for the suggestions.

 

[Leo21]

Cold feed and vent arrangement wrong. This will have caused a build up of crud in the surrounding pipe work, causing it to suck down the expansion.
Power flush plus pressurisation your best bet.