Normally they get louder with freer flowing exhausts/induction. My APS SR40 is bloody noisey but I wouldn't reccomend it!
Biggest increase in noise came from the silicone inlet pipe MAFless straight onto large cone filter.
I've got an old APS dump valve that whistles as it doesn't quite close properly!
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2005 Spec B 6MT - KiDO tuned (~270Bhp)
Custom exhaust - Cosworth filter - Samco Intake - Tints - Bilstein B8/B6 & STI springs - SuperPro ALK - Whiteline positive shift kit, rack mounts, rear adjustable camber bushes, front ARB mounts & strut brace, 20mm rear ARB with AVO mounts, - Hardrace Gearbox and pitch mounts - Prodrive PFF7's - Front Brembos - Kenwood CarPlay - 1/2 carbon grille - STI front splitter
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