02 Nissan sentra has trouble starting

Hello! I am having issues with my 02 Nissan Sentra turning over when I am starting the car. First for some background my car has almost exactly 115k miles on it. I have noticed the problem is getting slowly worse and worse. What happens is when I turn the key the engine makes a slow grrrr and rev sound, then a slighty faster grrr and rev, followed by a faster one before it finally turns over. There have been instances before when I have have to give it a good two or three times before it would turn over at all. I am not sure what is causing the problem. I do have one idea is that recently my gas mileage has been going down so I added Techron from the auto shop before 2 of my last 3 fillups (I didn’t on the last fill up since I was having the issues) Could that cause the problem? Other than that I am thinking maybe something with the battery (its a bit over 3 years old) or the spark plugs or fuel pump would be my best bet? ANy ideas?

I tried to take an audio recording of the issue but you have to really turn up the volume to hear the low lever grrr and revs before the car starts.

“…when I turn the key the engine makes a slow grrrr and rev sound…”

Do you think this “rev sound” is the starter motor spinning? I don’t know what could be revving if the motor hasn’t started yet.

How old is the battery.
It sounds like you have a weak battery or a bad connection at the barrery , or the opposite end of the cables