Stock exhaust change of sound question

[McDoof]

For some reason the sound of my car has changed.
MY05 3.0 RB 6MT
I am just running the full stock exhaust I cannot find any holes in the exhaust. I have lost the deep boxer purr when cruising around in 6th gear @ 1200rpm and it sounds a bit more like a normal V6 engine. A bit harsher. It sounds much like it did before once I get above 3000rpm. Just a bit louder than before.
Any ideas? I am thinking maybe the stock cats are just toast. Maybe I have just blasted out the insides of them. I am pretty sure the previous owner of this car drove it like a Nanna.

[Shiv]

Any vibrations?

[McDoof]

Not really, it just sounds different
Seems a little less torquey down low but that could just be me expecting too much. Might be worth getting some logs to Matt to see if he can see anything.
It feels like I have a hole in the exhaust, but I cant find it blowing anywhere.

[Curley5959]

Vacuum leak? The top of the rear air intake (that goes onto the throttle body) is known to split up the center. Not sure if this would affect sound though. Have you noticed a change in performance?

[HardwareBoB]

Vacuum leak? The top of the rear air intake (that goes onto the throttle body) is known to split up the center. Not sure if this would affect sound though. Have you noticed a change in performance?

[McDoof]

Pulled the whole intake out and it looks good to me. From air box through to throttle body. Will see if I can get it on a lift some time. I think the performance is down a bit.

[Curley5959]

Pulled the whole intake out and it looks good to me. From air box through to throttle body. Will see if I can get it on a lift some time. I think the performance is down a bit.

May have to have a smoke test done. No-one in my area was capable of doing a smoke test so I made my own. Paint can, two pipes coming out, one blew air into paint can, other connected to pipe that went into air intake. Inside paint can you burn a rag for 30 seconds or so and put it out. Whilst it is smoldering you connect a compressor to one pipe to blow air through, which blows the smoke through the pipe and into your intake. As long as everything is sealed up, it should work fine. If you see smoke pouring out somewhere, that's your leak.

Its also possible an exhaust gasket could be causing a vacuum leak. Again, easy test is smoke test up the exhaust. Block one off and pour smoke in and see if there are leaks.

[McDoof]

So the exhaust is definitely not leaking. 100% sure of that one now. Had the car up on a hoist to get the 3rd cat deleted and went through the whole system.
This may sound like a bit of a long shot, but could it have something to do with the oil I am using? I think this change in sound may coincide with the last oil change.
I am not consuming any oil. 5000km since the last change and still not a drop missing, but I had the engine flushed the last time had the oil changed and I switched to full synthetic oil too. I might just be clutching at straws here.

The next step is a smoke test on the intake I guess.

[Troy]

Baffle plate?

[Shaheenis]

If the cat has failed it will feel a lot more sluggish and sound will change. Muffler baffling can also break down but never happened to me.

[hmhaga]

I've noticed that the engine note changes when IAM drops below 1.0 (ignition timing retarded), it results in a "softer" engine note.
Didn't actually notice this until my car was remapped, and IAM increased from 0.5 to 1.0 (it had been stuck at ~ 0.5 its entire life).

The IAM typically drops because of engine knock, in my case because of running on 95 RON fuel.

[McDoof]

Last I checked the IAM was still at 1. I am running on 98 with Kido tune. Although I think your description of the sound is probably bang on. It's a bit softer. More noticeable when the car is cold. Almost lacking a bit of bass.

[Robbks]

has there been and ECU revision in there,
different timing values, AVCS points and idle control changes the exhaust note

[McDoof]

has there been and ECU revision in there,
different timing values, AVCS points and idle control changes the exhaust note

Not recently no. Waiting for Matt to come to NZ to finalise the tune.
I think the only thing that changed was the move to full synthetic oil and I had a full engine flush done at the time. So maybe it's just cleaner

[McDoof]

Hah, I think I finally cracked this nut. Stupid in the end.
There is a rattling exhaust shield. The high frequency sound it makes intrudes on the nice low rumble the engine makes. It only happens under certain engine load situations to get the right vibration. I only really picked it out while I was sitting in the drive thru the other day with the window down. Amazing what you can hear when you have lots of reverberation surfaces around you.