Catalytic Converter exhaust question

Hi Guys

Have noticed car sounds a little louder than usual, and has lost a little power, fuel economy ever so slightly down too, no smoke though under acceeration.

Window down whilst driving sounds like coud be exhaust blowing,

at idle sounds fine.

Had car on ramps been and checked exhaust front to back and all seems fine, no rot, rust or holes.

if i squeeze mesh where I assume is where CAT is it does slightly change tone of exhuast and sounds a little blowy/muffled i suppose, but when i let go sounds fine. What are symptoms of a CAT failing or failed anyone know??

Also for the two years plus had car under hard acceleration there has always been at high revs a kinda rattling rasping sound from engine, does not smoke, pulls like a train and MPG early 50's. Is more mechanical than a blowing sound, not disimilar to a impellor sound from turbo when they showing sounds of wear. (Had one go in my Nissan 200 turbo many yrs ago). Sound only apparent at high end of rev range, turbo comes in as it should. No smoke at all from car, doesnt use a drop of oil, never has.

This sound has got slightly more noticeable, this occured at same time as I noticed what I suspect maybe exhaust blowing.

Anyone shed any light on this for me.

Car has Synergy with piefburg MAF, EGR Mod and PCV filter changed, serviced 2000 miles ago, car done 142,000 miles with extensive FSH.

Have not checked Viton O rings, not sure where or what I'm lookin for with these, see they get mentioned regularly.

Any help would be much appreciated, thank you..... '',)

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