Hp 4345 printer that is picking up multiple sheets from tray2

Frankly speaking, this problem exists and printer companies always have denied this. What I think from my experience that there is some engineering problem with all these printer, in the way paper is fed in.Still I give some solution which HP's site suggests. See if it works in your case:
hp 4345 printer that is picking up multiple sheets - s.gif

Issue Multiple pages feed through the printer when printing. Solution If the printer is picking up multiple sheets of paper, follow the recommendations below:

• Keep more than 10 sheets in the In tray.
• Ensure media is not loaded too far and extending past the In tray.
• Store all media in a dry, cool place. Humid climates will see this issue more often.
• Do not print on media that has already been printed on. The dampness of the ink will cause pages to stick together.

1. Remove the media from the In tray.
2. Fan the edges, re-square the media, and reload the media properly into the In tray.
3. Slide the paper width guide to the right until it stops at the edge of the media, then push the paper length guide towards the paper until it stops.
4. 
   NOTE: Not all HP Deskjet printers have rear access doors. Skip this step if your printer does not have a rear-access door. Remove the rear-access door (if applicable) and clean the internal rubber rollers with a soft lintfree cloth moistened with distilled water. Wait until the rubber rollers dry and replace the rear access door.
5. Verify that the correct media size and type is selected in the printer settings along with the appropriate quality.
6. If this issue still persists, try a different type of paper.