Windows 7 - What is the reason for the spin up and heat increase?

This has just started recently, my computer tends to make a loud sound as though something is spinning incredibly fast. When I feel the top of my case when this happens, it is hotter. When feel the copper tubbing on my CPU fan, it's hotter. When it spins down, everything cools off to the touch. My CPU and PSU fans are both running, it is an older PC, it would not surprise me if something is, slowly dying.

Could be something as simple as a malware scan done on startup or at regular intervals, if it is a laptop might be dust, dirt, etc.

Is your HDD activity LED active during this time, i.e. can you tell if the PC is actually doing something CPU-intensive in the background? You'll want to open Task Manager and see if something is making your CPU crazy, and spinning-up all fans. Obvious idea alert: make sure too there isn't a disc in your CD/DVD drive(s)!

A good cleanup of the box may also help.

It began after doing a good clean up of the box.
I'll check the HDD activity LED, next time it happens which I can't predict when.

You could also check msconfig/startup using the search and see if you have a lot of things starting up.

Check whether any of the fans may have come loose in the process.

Sounds like the CPU cooler is not seated properly or if you removed it and didn't re-apply thermal paste to the CPU.

I agree with the above, clean the case and blow out the fins on the coolers then if still acting up them remove cpu cooler and clean all surfaces noting the condition of the thermal compound, re-apply and mount. Run Anti-Virus and Malware Bytes in Safe Mode as well as checking unneeded items in Start Up as mentioned then report back.

It could be to that, I've had two Services that i do not need starting up randomly that are a bit of a Pig with resources. When they started up on both my laptop and desktop both Windows 7 they would run hotter until the service stopped its self. Now disabling the two services are not always going. If you are doing stuff such as: Video editing, photo editing that kind of stuff then you do not want to delete "stisvc" but the next one you can delete if you DO NOT have a table or a touch screen or any kind of touch device pluged into your computer. the service name is "TabletInputServic" And iPhones and iPod Touchs DO NOT COUNT. If you want to try this you have to run CMD.exe as admin, then type in SC Delete Service name here and hit enter and if done right it will work... You also need to make sure you you stop the service from the service's windows with in windows. Now i am not saying this is the problem for you but this is what made both my systems do this on me and that's what i did to fix it.

P.S becare full what services you Delete tho. the two i listed are safe to delete.

Hope this helps
RitualJman