The German Football Federation (DFB) launched an inquiry on Tuesday into allegations Hoffenheim employees used a sound system to drown out chants from Borussia Dortmund's fans during a German league match.
German champions Dortmund lost 1-0 at Hoffenheim on Saturday and daily newspaper Bild shows pictures from the game of a device next to the bulk of Dortmund's fans in the Hoffenheim stadium which reportedly drowned out the singing from the visiting fans.
A Dortmund fan has lodged a complaint with local police, claiming the noise generated by the machine -- a portal public address system -- was so loud it brought on tinnitus.
"Right now, we are launching preliminary inquiries to clarify the exact facts," DFB media director Ralf Koettker has said.
The Hoffenheim employee is said to have used the machine after Dortmund fans sang songs aimed at Hoffenheim's mult-millionaire owner Dietmar Hopp.
"In his own words, the employee wanted 'an antidote' against the insults towards Mr. Dietmar Hopp which he felt were no longer tolerable," said the club in a statement.
Local police have confiscated the device, while Hoffenheim have identified the employee responsible for bringing it into the stadium and are taking disciplinary action.
"We will examine statements from the aggrieved and the club about the alleged perpetrator," a police spokesman told SID, an AFP subsidiary.
"The complaints are directed towards Hoffenheim, but the fact the club has informed us the person involved acted independently means we will focus our investigations on him."
A second Hoffenheim employee later reported himself to police on Tuesday after being involved in installing the device at the stadium.
There are claims the device was also used in Hoffenheim last season during a German league game with Eintracht Frankfurt.
Hoffenheim owner Hopp has said he knew nothing of the device and was against it being used in his team's home ground.
"It would be grotesque if we were to try and fight the chants from rival fans in such a way, because it would only stir up the environment more," Hopp told German daily paper the Rhein-Neckar-Zeitung.
"For us, it is important that Hoffenheim has a good relationship with the other Bundesliga clubs and this should not be disturbed by a minority of fans."