Reduction of Exhaust Noise by Means of Thermal Acoustics
"...We observe about 2 dB decrease of the OA dB value when the gas temperature decreases of about 100°C..."
https://sci-hub.ru/10.4271/2012-01-0804
NB that a 3 dB decrease in noise is perceived as
'half as loud' by our human ears..!
(logarithmic scale and all that too)
Surprising is the dB decrease @ lower frequencies too!
(This is a Sci-Hub link: Sci-Hub is a database of research that's normally behind a paywall.
As it's your 'tax dollar' (or money you spent on a car etc) paying for the research; you have already paid for the info in their (and my) opinion.
If you type in Sci-hub as a search you will find more than 1 site where you can paste in the heading of a paper you are interested in. This is because the 'Paywallers' spend a lot of time and money trying to get it shut down, resulting in multiple copies of the site that aren't always synced.
In my experience if the 1st 'Sci-Hub' you try doesn't find the paper, the second or 3rd one may well find it)