The GROZA experiment detected bursts of low-frequency radio noise similar to those generated by lightening storms on Earth, but significantly more intense. There is some evidence that they originate in the deep atmosphere, far below the cloud layer. Lightning strikes around volcanic eruptions or some unknown atmospheric electrical phenomena could be responsible. It detected intense electrical activity during the descent of Venera-11, but much less from Venera-12, indicating that thunderstorms may be localized events on Venus as on Earth.
http://www.mentallandscape.com/V_Venera11.htm
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1982PAZh....8..419K&db_key=AST
Space/Science » in reply to Yes, you're right. Venera recorded sounds during descent
A chart and some details on the Venera 11-14 GROZA experiment
