Hiya guys, you might have already solved the problem, but I have a 2014 Seat Ibiza Fr Edition 140 remapped at stage 1, I noticed I had this issue whilst driving at 90mph, I do have a plastic sump guard which has snapped and been DIY repaired by a tie wrap technician 
I am going to buy a new sump guard eventually but for now I will take it off and rinse and repeat to see if it is the problem, I will get back to you if it is and hopefully it helps you pin point where your problem is
I didnāt even know I had a problem.
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I donāt have any problems. Iām perfect in every way. 
As for your problem, replace the sump guard and go from there. Itās the obvious first step.