Start by checking the negatives, not just the scans. Scanning and printing can change the look, so the negative is the best place to diagnose the issue.

If the clear orange areas between frames and the edge markings/frame numbers look normal and readable, the film likely was developed properly and wasn’t heavily fogged by light. If those areas are unusually dense or dark, the film may have been fogged or processed incorrectly.

Assuming the film was developed and scanned properly, the look you describe—muddy gray tones, noise, low contrast, and poor clarity—strongly suggests severe underexposure. On color negative film, underexposed frames often produce thin negatives and scans like this.

So the most likely cause is exposure error in-camera, but you should confirm by inspecting the negatives. If they look thin, that points to underexposure. If the edges and rebate look abnormal, then processing or fogging is more likely.