poppong noise from air vents in 95 420E

Just bought a 95 420E with 78,000 miles and there is a popping noise coming from the dash airvents when the heat is on. The noise occurs every 6 seconds. Has anyone had this problem?

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@verizon.net says...

Yes. In a 1981 300 SD. But since I am deaf, the noise does not bother me. Sounds like something opening and closing at regular intervals.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.