Run slowly but with noise that's excessive? (4,4)
I believe the answer is:
tick over
'run slowly' is the definition.
(I've seen this before)
'with noise that's excessive?' is the wordplay.
'with' is a charade indicator (letters next to each other).
'noise' becomes 'tick' (I can't justify this - if you can you should give a lot more credence to this answer).
'that's excessive?' becomes 'over' (over can mean in excess or excessively).
'tick' put next to 'over' is 'TICK OVER'.
'but' acts as a link.
Can you help me to learn more?
(Other definitions for tick over that I've seen before include "Just keep going like idling engine" , "(Of engine) idle" , "(Of engine) run slowly in neutral" , "Run smoothly (or very slowly?)" .)