Galaxy S5 9 months old. Seems to have suddenly slowed down. My viral scan tured up no results. Is it adware/malware? Is there an APP for that or another process to use to get rid of it?
If Malwarebytes and an antivirus app didn't find anything, I doubt it's malware. (Adware doesn't slow a phone down much.)
It's still under warranty, so back everything up and contact whomever you contact in your country to have it replaced/repaired. (In the US, the carrier will usually replace it - with a refurb, considering its age. [Have no worries - my current refurb is over 2 years old.])
It's probably an App. Disable or delete any App you don't use.
I'd advise wiping the device and starting fresh before trading the phone in. Slowing down over time is definitely a software thing, its not like the SoC is getting slower on you.