Contamination on GC-FID

Hi Everyone

I work with an Agilent GC6890N and since the beginning of the week, we have a contamination (one peak) in our system which I have no idea where it comes from. I have a picture:

This is a blank run with solvent MTBE (2-Methoxy-2-methylpropan). On RT 1.25 you can clearly see the contamination. 

First i did, was an instrument blank run (split injection), which was clean.So i assumed it comes from the injection or outside my system.

Here is what i tried:

- Fresh/other solvent

- Syringe cleaned/replaced

- Septa and liner replaced

- Wash vials, ans septas cleaned/replaced

- cleaned the inlet

I even did an run with empty vial and the peak is still present, so no solvent issue.

Has anyone another idea, from where this peak can come from?

Thanks in advance and have a nice day! 

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