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New plugs = noisier engine ? (Corolla) - arnold2
Just had the platinum plugs in my Corolla 1.4vvti with Iridium jobs from sparkplugs.co.uk - however, I have noticed the engine sounds a bit different - a high pitch sound, not that loud. Can different plugs change the engine sound, or has the garage done something wrong ?!
New plugs = noisier engine ? (Corolla) - Altea Ego
Two possible reasons
1/ Plug not tightened and is leaking with a whistling sound.
2/ Plug noses too long and knocking holes in piston crowns.

Probably 1/ as 2/means you would have found out by now.
New plugs = noisier engine ? (Corolla) - arnold2
Sounds like such a basic thing tightening plugs I'm amazed they could have got that wrong ! Will take back to Garage !
:-(