high pitch noise at the start

[redcore]

i have this little portable compressor Badger TC910 ASPIRE PRO with 3l air tank. its a small compressor. i have used it for couple of times without any troubles, but now when i turn it on it's giving me some weird high pitch noise which goes away after couple of minutes. it sounds like a dry piston moving in a cylinder - you know when there is like some kind of a friction) but the thing is that it is an oil free diaphragm compressor (or it should be). any advices please?

sound file attached. just rename that "pdf" to "m4a and play it in "vlc media player"


thanks!
rob
View attachment compressor_rename_pdf_to_m4a.pdf