I know we have to put up with adverts to help pay for the site but now I am getting ads top and side for Ducati Been there and ain't going back!
A lot of banner ads now are tailored to you using your browsing history. They call it remarketing where they basically show you adverts for things you have looked at before. Its the same reason some of us seem to get triumph knickers and bra ads popping up because we have googled triumph (or women in knickers and bra depending on what you wanted to look for). One of those things I'm afraid just another way got marketing companies to try to get more money out of you! Sometimes with remarketed ads you can click a cross in the top corner of the ad to show your not interested this should change the ad then to something generic.
Exactly as Spankyham has said, I think they are part of the forum design and they can only be modified and not turned off....