Mercedes GT Roadster belt squeal issue

A squealing serpentine belt often points to a tensioner issue. A failing tensioner can cause belt slippage, leading to noise and potentially reduced performance. Have you inspected the belt itself for wear or damage? Sometimes a worn belt can mimic a tensioner problem. Is the noise constant, or does it vary with engine speed? It's difficult to diagnose precisely without hearing it, but your suspicion about the tensioner is a reasonable starting point.

I've visually inspected the belt, and while I don't see cracking or fraying, it does appear somewhat glazed. The noise is most pronounced during cold starts and diminishes as the engine warms, though it remains subtly present, varying with engine speed. Does this further solidify the likelihood of a defective belt tensioner, or are there other potential culprits before replacement

The fact that the noise diminishes as the engine warms up does lean towards the tensioner. When cold, the rubber in the belt is stiffer, and a weak tensioner might not be able to provide enough pressure. While other things could contribute, like a misaligned pulley, the glazed belt and the temperature sensitivity really point to a tensioner issue. Given your description, I'd say it is time to consult a workshop.

I consulted with a qualified technician. The diagnosis confirmed a faulty belt tensioner. Replacement of the tensioner, along with a new serpentine belt, resolved the belt squeal and restored proper engine performance. The final cost aligned with my initial estimate. I appreciate the guidance towards the correct resolution.