[Partial QUOTE=Xilliah;15196298] ...I'll ask the LBS to check all the spokes this time. Antoon[/QUOTE]

OP; Recommend being a good bit more specific. Do you want them to could the spokes to make sure they are all there? Or something more useful? Need to ask specifically if the LBS has a competent wheel builder on staff who regularly builds successful wheels. If yes, then talk with him/her one-on-one. Tell them what is happening to your wheel. If they suggest that you hand the wheels to them for a re-truing and full tensioning service, let me. Be prepared to pay for the service ($30-50USD). From your description, your wheels are basic machine built wheels that lack a correct tensioning service. Until that is done, the wheels will regularly require fixing and never perform well. Your story also seems to indicate that you are not visiting a good LBS and you might do well to find another one.