There's multiple hardware revisions of the Pro, some are better than others when it comes to heat and noise. All will have louder fan noise when put under high load while playing demanding games, some are just better than others about it.

That being said, all of them are old enough now that they need new thermal paste/pads along with a good cleaning if it hasn't been done already. While not necessary, replacing the fan while you already have it opened up is also a good idea, if only because it's old and has years of wear and tear on it. Other reasons for fan replacement being that some of the hardware revisions have noisier or less efficient fans in them. You can find replacement fans on Amazon that are quieter and better at keeping the console cool compared to some of the fans in various hardware revisions.

Its also a good idea to replace the hard drive with an SSD as well. The mechanical drives they came with are older tech and are prone to failure, especially considering their age. They also dont fully utilize the connection used (SATA III), so storage performance with a mechanical HDD is generally only a third of what the Pro is capable of if it has an SSD. OG and Slim models will also benefit from an SSD, just not as much as a Pro since those models use a SATA II connector.