Is there something wrong with my car or should I be worried? Can someone help me with this mystery?

After my oil change and tire rotation I notice a low humming from the front of my car I thought it was a bearing going bad it sounded like that. I figured it was my tires because I haven't rotated them and 10,000 miles and I usually rotate them every 5000 miles. I put on about 2500 miles since the rotation so... show more After my oil change and tire rotation I notice a low humming from the front of my car I thought it was a bearing going bad it sounded like that.

I figured it was my tires because I haven't rotated them and 10,000 miles and I usually rotate them every 5000 miles.

I put on about 2500 miles since the rotation so I'm thinking maybe the noise is going away because they are starting to even out.

However I noticed my coolant was very low like even below the L but when I pulled the hose out there was coolant dripping out of it so it was definitely cycling through the engine and my temperature has never been hot.

Not sure how long it's been like this for but the hum has only been going on for about 4,000 miles starting off low and getting higher.

I added coolant and filled it up to the full level and I even topped off the hybrid coolant which was only slightly low.

I've noticed that my engine does not kick on as much anymore and the noise has pretty much vanished although I still hear it ever so slightly this is why I cannot figure out if adding coolant did it and if so why or maybe it's just the tire starting to even out? Can someone help me with this mystery
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