Gen2 MS3 - Louder engine braking growl at 2600-3000 RPM + shutdown noise

[yyspeed]

Hey everyone,

Looking for some opinions before I start throwing parts at the car.

Car:

• 2013 Mazdaspeed3
• ~155,000 km
• Cobb SF intake
• No CEL or stored codes

Issue #1

During engine braking, above about 3000 RPM, the car sounds normal at first, but as the revs pass through roughly 3000-2600 RPM, the engine suddenly gets significantly louder and deeper (almost like the engine note jumps up a few levels), then returns to normal below that RPM.

It sounds like a normal engine growl, just much louder for that specific RPM range. No grinding, squealing, or metallic knocking.

I think I may hear a similar change in tone while accelerating through the same RPM range, but it's much harder to tell.

Issue #2

On shutdown, I get a brief "tak-tak-tak" (about 3-4 light metallic taps) as the engine comes to a stop. It only happens during shutdown.

These have been happening for a few months (yes i know bad owner).

Has anyone experienced this combination of symptoms? I'm wondering if the 2600-3000 RPM noise is just intake/exhaust resonance (Cobb SF), engine mounts, or if it could be related to the timing/VVT system.

 

[Easter Bunny]

I would start by checking engine mounts. With the hood open have someone try to move the car with the parking brake engaged. If the motor moves its a mount

 

[Enki]

Sounds like engine braking on decel for issue 1. If it consistently happens no matter the operating conditions within that RPM range, maybe check all your exhaust connections.

Not sure on the second, unless it happens when the engine is completely stopped, in which case, could be the throttle body doing tests.

 

[DatsunZ]

Issue 1:
If you have a completely stock exhaust it shouldn’t be very noticeable unless you are used to luxuriously quiet vehicles in general.

I have a Speed6 and This was something I noticed after I replaced my stock exhaust with a custom built 3” stainless exhaust. I went from fully stock to a cat-less down pipe, a 200cpi catalyst in the factory secondary cat position, and split the 3” to 2x 2.5” pipes each with a resonator/muffler after the rear axle. I immediately noticed the engine braking resonance at 2500-3000RPM. It is annoying for sure and is most noticeable in gears 2-3-4.

I attribute this to engine braking being a pretty raucous event for engines in general. Your cylinders go lean and start fighting other forces, so I believe this comes from that rev range being where the engine vibrates the most as all the forces add up, so any worn engine mounts start buzzing and the thinner-walled/unshielded new exhaust parts are louder while this happens causing constructive inference with the vibes which leads to a very loud cabin noise. I have the whole Damond Motor Mount set, but have only installed the RMM currently, so my 150k mile originals are certainly not isolating vibrations the way they used to. It only bothers me when I have the windows up, which is only on the highway with a passenger, or when temps are >95F or <40F so I haven’t thought too much about rectifying it. Using A/C increases these sounds due to the extra load it places on the engine.

I would start by doing exactly what Easter Bunny and Enki suggested above, and then (if you have a aftermarket exhaust) get at least 1x high flow cat, 1x 12-18” resonator, and 2x turbo/baffled mufflers depending on your taste for sound.


Issue 2:
Do you drive with A/C on pretty much all the time?