Police in north Devon are investigating two thefts of catalytic converters from commercial vans, saying the crimes are "unusual offences".
The first was taken from a Peugeot Boxer van in Bear Street in Barnstaple between Saturday and Monday.
Another converter was stolen between Saturday and Tuesday from a white Citroen Relay van in Ashleigh Road in the town, police said.
The exhaust systems are known to contain precious metals.
Pc Terry Hodgson, of Devon and Cornwall Police, said: "These are unusual offences within the Barnstaple area as they are specialist items that may have already been offered for sale".
Officers said they believed the exhaust systems were being targeted to be sold on because of precious metal inside them, including platinum, and other metals such as rhodium and palladium.