I tried out one of my upright bass VSTs, and it has this slight buzzing sound in it, which is probably meant to simulate the sound the strings make when they hit the fingerboard during a harder strum.

So, it seems to be a natural sound effect and not a serious clipping artifact in the sound (you can still check to see if there’s any additional clipping distortion - preferably with a true-peak meter, which records level peaks, including inter-sample peaks, much more accurately).

Nevertheless, this buzzing is much louder in your case than in the one I tested.
Could it be that you have a strong compressor effect on the double bass that also brings such background noise up to the same volume level as the primary instrument sound?

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Normally, it’s not common to mix the bass range so that it fills the entire stereo field.

But in this case, it sounds really great and powerful, which fits the composition perfectly.
The drums and other instruments also come through really well in the context of the double bass.
So as long as there are no frequency conflicts and you don’t want to create a different spatial setup for the soundtrack, you don’t necessarily need to reduce the stereo width of the double bass.

However, if additional instruments in the bass range are added later in the composition and really start competing for the lower frequencies, you can try panning the entire double bass to the center (center mono, with no involvement of the left or right side) and then panning the corresponding reverb, without any center involvement, hard to the sides via aux send, using an aux send with a suitable low-cut filter.

This allows the impact of the bass instrument to come through extremely well, while the reverb, panned hard to the sides, creates the impression of a wide, room-filling sound that also has a clean bass range.

I once conducted an interesting sound experiment regarding stereo width in my mixing thread here on OC-Remix - in case you're interested (it's my post from December 20, 2024, titled “Using specific stereo widths for instrument and direct signal tracks for more clarity and assertiveness in the mix and for a more impressive representation of panorama and spatiality in the soundtrack”):